Pechini Method Research Articles

The structural, optical and magnetic property of iron oxides submicron particles synthesized by the Pechini method from steel industry wastes

A new value-added at submicron scale was developed from industrial wastes via the Pechini method using a ferric oxide (iron/steel husk lamination) precursor from steel industry. The analysis of all synthesized samples was carried out by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, UV–Vis/DRS analysis, Fourier-Transform infrared spectroscopy and Raman spectroscopy. X-ray diffraction and scanning electron microscopy exhibit the structure, morphology, phases and the purity of the samples studied. The crystallite size was estimated for each thermal treatment. Vibrating sample magnetometer study shows high saturation magnetization for the sample at 500 °C with respect to the other samples. For this sample, the energy band gap was determined by using two methods to avoid false conclusions. Also, a detailed study by vibrational spectroscopy was carried out on the local structure of the sample. The sample treated at 500 °C exhibited a higher saturation magnetization of 55.1 emu/g compared to the sample treated at 300 °C (45.5 emu/g).

Tin, niobium and tin-niobium oxides obtained by the Pechini method using glycerol as a polyol: Synthesis, characterization and use as a catalyst in fructose conversion

The selective and efficient conversion of fructose into chemicals has been extensively explored, especially from the perspective of a more sustainable industry based on renewable inputs together with a more environmentally friendly process. In this study, mixed metal oxides based on tin and niobium were synthesized by the Pechini method, replacing ethylene glycol with glycerol, a renewable chemical. This replacement allows the use of pure or mixed oxides exhibiting high specific surface areas but did not lead to significant differences in the amount and nature of the acid sites present in each case. Furthermore, the mixed oxides had increased numbers of Lewis acid sites, while the number of Bronsted acid sites decreased. Catalytic tests performed at 150 °C demonstrated that the use of these materials leads to conversion results higher than those observed for pure oxides (SnO2 (EG) = 48.3 %, Nb2O5 (EG) = 51.6 % and SnO2 (G) = 56.8 %, Nb2O5 (G) = 59.6 %) because 78.5 and 75.7 % consumption of fructose for SnNb (EG) and SnNb (G) was attained at 2 h, respectively. In addition, the catalysts show promising 5-hydroxymethylfurfural (5-HMF) selectivity, and the presence of lactic acid was also detected. In addition, recycling experiments were performed, and stability was observed for 4 cycles without structural change in the catalysts.

Effect of microwave heating during evaporation solvent and polymeric precursor formation in synthesis of BaZr0.08Ti0.92O3 nanopowders

The aim of this study was to verify the effect caused by microwave-assisted heating used during evaporation solvent and polymeric resin formation in the crystallization and final characteristics of BaZrxTi1-xO3 (BZT) nanopowders synthesized by the polymeric precursor - Pechini method. Using microwave heating, the syntheses were evaluated in acid and basic pH. For comparative effects, the syntheses using both pH were also carried out with conventional heating. Microwave heating allowed a reduction of more than 80% in the duration of the solvent evaporation and polymeric precursor formation steps compared to conventional heating at the same temperature. XRD and Raman spectroscopy confirmed the formation of a mixture of cubic and tetragonal perovskite structures with a high purity level of BZT. The most promising results were achieved, mainly when comparing the syntheses with basic pH, where BZT was crystallized at lower temperatures than those of conventional heating and acid pH achieved the highest degrees of crystallization and purity, as well as smaller average particle sizes. The calculated energy values for crystallization of the BZT synthesized by the microwave-assisted method were lower than those obtained by the conventional method. We also observed a favorable influence of microwave heating in obtaining smaller nanoparticles with uniform morphology and narrow particle distribution for this material, mainly for synthesis in basic pH.

Metal-oxide stabilized CaO/CuO composites for the integrated Ca/Cu looping process

An integrated Ca/Cu looping process has been proposed recently for CO2 capture. It uses the exothermic in-situ reduction of CuO with methane or natural gas to supply the heat required for the endothermic calcination of CaCO3 to regenerate CaO for the following CO2 sorption cycle via bifunctional CaO/CuO composites. CaO/CuO composites possess excellent redox characteristics, but the rapid decline in CO2 capture performance remains an unresolved problem. Two different types of stabilizers, i.e., Al2O3 that can form a mixed phase with CaO, and MgO that does not form a mixed phase with CaO under reaction conditions, were incorporated into CaO/CuO composites via a Pechini method, and investigated by thermogravimetry. The results showed that the incorporation of Al2O3 or MgO enhanced cyclic stability significantly, and the formation of calcium-aluminum mixed oxides improved the cyclic CO2 capture stability more than did MgO. The best performing Al2O3- and MgO-stabilized CaO/CuO composites exhibited CO2 uptake of 0.14 and 0.09 gCO2/gmaterial after ten repeated cycles, exceeding the unstabilized CaO/CuO composites by 100% and 29%, respectively. We observed that 15 mol. % Al2O3 is the optimal quantity for Al2O3-stabilized CaO/CuO composites, ensuring a high and cyclically stable CO2 uptake capacity (0.11 gCO2/gmaterial after 45 cycles). Moreover, the cyclic stability was enhanced remarkably with increasing carbonation/oxidation temperature (from 550 to 750 °C). In-situ X-ray powder diffraction results suggest that the intermediate phase Cu2O played an important role in the enhanced performance of the composites at high carbonation/oxidation temperatures.

Crystallization kinetics of binary Yb2O3–Al2O3 glass

The ytterbium aluminum garnet composition YbAG (62.5 mol.% Al2O3, 37.5 mol.% Yb2O3) was prepared in the form of glass microspheres by flame synthesis. Precursor powder for flame synthesis with high homogeneity was prepared by modified sol–gel Pechini method. XRD pattern of prepared glass microspheres indicated predominantly amorphous nature of the sample. Detailed study of morphology of the microspheres by scanning electron microscopy revealed the presence of a small fraction of partially or fully crystallized microspheres. The high-temperature X-ray powder diffraction analysis (HT XRD) was carried out in the temperature interval 750–1450 °C: The temperature dependence of phase composition was determined. Crystallization of Yb3Al5O12—ytterbium aluminum garnet phase—was observed in the temperature range 900–1200 °C. The DSC analysis with heating rates 2, 4, 6, 8, 10 °C min−1 in temperature interval 25–1200 °C was performed in N2 atmosphere to study thermal behavior and crystallization kinetics of prepared glass microspheres. The two exothermic effects at 918 and 939 °C were observed, which were attributed to Yb3Al5O12 crystallization. The crystallization kinetics of prepared sample was examined with the use of JMAK model, and the kinetic triplet—frequency factor A = (1.8 ± 2.2) 10+28 min−1 (for the first peak), A = (1.2 ± 1.6) 10+55 min−1 (for the second peak), apparent activation energy Eapp = (6.4 ± 0.1) 10+02 kJ mol−1 (for the first peak), Eapp = (1.3 ± 0.1) 10+03 kJ mol−1 (for the second peak) and the Avrami coefficient m = 3 (for the first peak) and m = 2 (for the second peak)—was determined using RSS, Radj2 , AIC and WAIC criteria.

Structural and Magneto-Electrical Properties of Bi2-xSmxSr2CaCu2O8 + δ High Tc Superconductor Prepared by Pechini Method

Polycrystalline superconducting samples of Bi2-xSmxSr2CaCu2O8+δ were synthesized using Pechini method with different doping Sm concentrations (x = 0.0, 0.05, and 0.10) and investigated. FTIR spectroscopy showed that our final samples are totally free of organic elements. Le Bail refinement revealed that they were crystallized in the Bi-2212 phase. A small amount of the omnipresent Bi-2201 phase appeared as an impurity phase in all samples, whereas a small amount of Bi-2223 appeared only in the case of x = 0.5. In one hand, the Sm doping decreases the cell parameters, and in other hand, it leads to a transformation into a pseudo-tetragonal structure in the case of x = 0.10.The modulation was found to be incommensurate and increases with Sm content. The magneto-electrical resistivity curves show a transition to the superconductor state. The critical temperature TC decreases with the Sm doping, whereas the activation energy U0 increased from 53.4 meV to 68.9 meV.

Performance evaluation of highly active and novel La0.7Sr0.3Ti0.1Fe0.6Ni0.3O3-δ material both as cathode and anode for intermediate-temperature symmetrical solid oxide fuel cell

In comparison to various power generating devices/energy conversion systems, solid oxide fuel cell (SOFC) has received much attention due to its remarkable efficiency, reliability and low pollution. Modified pechini method is used to synthesize La0.7Sr0.3Ti0.1Fe0.6Ni0.3O3-δ (LSTFN) perovskite material and is utilized as cathode and anode for intermediate-temperature symmetrical solid oxide fuel cell (IT-SSOFC). The X-ray diffractometer (XRD) patterns reveals perovskite cubic structure with single phase for LSTFN. The maximum conductivity ~318 Scm−1 is obtained for LSTFN in air at a temperature of 700 °C, but is decreased with further increase in temperature due to small polaron mechanism. However, the conductivity is enhanced up to ~1.1 Scm−1 at the same temperature in the presence of dry H2, being capable to be utilized both as anode and cathode. Low polarization resistance (Rp) ~0.047 (with air) and 0.201Ωcm2 (with dry H2) is exhibited by as prepared perovskite material at a temperature of 800 °C. The fabricated symmetrical cell maintains good stability with no apparent degradation during the tested hours ~300 in air and ~100 with dry H2.

Novel Ni/Ce(Ti)ZrO2 Catalysts for Methane Dry Reforming Prepared in Supercritical Alcohol Media

To achieve a high activity and coking stability of nickel catalysts in dry reforming of methane, materials comprised of ceria–zirconia doped by Ti were investigated as supports. Ceria–zirconia supports doped with titanium were prepared either via the Pechini method or by synthesis in supercritical alcohol media. Ni-containing catalysts were prepared by two techniques: standard incipient wetness impregnation and one-pot synthesis. The catalytic reaction of DRM to synthesis gas was carried out in the 600–750 °C range over 5% wt. Ni/Ce(Ti)ZrO2. Dried and calcined supports and catalysts were characterized by physicochemical methods including N2 adsorption, XRD, Raman, H2-TPR, and HRTEM. Both preparation methods led to formation of solid solution with cubic fluorite-like structure, as well as after addition of Ti. Introduction of Ti should provide improved oxygen storage capacity and mobility of support oxygen. The highest activity was observed with the catalyst of 5% wt. Ni/Ce0.75Ti0.2Zr0.05O2−δ composition due to optimized oxide support structure and support oxygen mobility.

Low-Temperature Decomposition of Nitrous Oxide in the Presence of 1%Cs/MgxCo3–xO4 (x = 0–0.9) Oxides

Mixed oxides 1%Cs/MgxCo3–xO4 (х = 0–0.9) with a spinel structure are synthesized by precipitation from nitrate solutions using (NH4)2CO3 as the precipitating agent and the subsequent modification of the dry precipitate with cesium by the Pechini method and calcining. The synthesized samples are studied by XRD, BET, SEM, TPR, and TPD methods. It is shown that an increase in the magnesium content leads to a significant decrease in the degree of crystallization of the oxides, an increase in the specific surface area, and the formation of loosely bound oxygen species, which contributes to an increase in the catalytic activity of the samples in nitrous oxide decomposition at temperatures of 150–400°С. The highest activity is exhibited by the 1%Cs/Mg0.1Co2.9O4 catalyst characterized by the presence of the maximum amount of loosely bound oxygen species. It is shown that the presence of oxygen or water in the reaction mixture leads to a decrease in the catalyst activity at 250°C by 10 or 80%, respectively; after that, the catalyst exhibits a stable on-stream behavior for at least 25 h. The catalyst activity is restored after a heat treatment.

Infrared Reflection and Transmission Spectra of MgAl2O4 Ceramic Spinel

IR spectra of magnesium aluminate spinel (MAS, MgAl2O4) ceramic are recorded in the wide ranges 50–1000 cm–1 (reflection) and 1000–5000 cm–1 (transmission). In addition, the IR reflection spectrum of crystalline α-Al2O3 is recorded in the range of structural bands. A comparative analysis allows the origin of a series of spectral bands appearing as a combination of vibrations localized on AlO6 octahedral and MgO4 and AlO4 tetrahedral cells to be clarified. Spectra of ceramics synthesized by both the hydrolysis of double Mg–Al isopropylate and a modified Pechini method are compared.

High Voltage Stability and Characterization of P2‐Na0.66Mn1‐yMgyO2 Cathode for Sodium‐Ion Batteries

AbstractThe development of sodium‐ion batteries is currently limited by the availability of high‐energy and low‐cost cathode materials. The energy density of cathodes can be maximized by expanding the voltage range for cycling, but this often leads to severe capacity degradation. Cathodes that demonstrate good long‐term cyclability at high voltage cut‐offs (>4.3 V vs Na/Na+) are scarce in the literature. In this work, layered P2‐Na0.66Mn1‐yMgyO2 was synthesized by using a modified Pechini method at various compositions (y=0, 0.05, 0.1) and characterized after extended cycling between 2–4.5, 4.6, and 4.7 V vs. Na/Na+. Na0.66Mn0.95Mg0.05O2 displayed a similar initial discharge capacity to Na0.66MnO2 with significant improvements in cycle retention. It was most promising when cycled between 2 and 4.5 V, retaining 140 mAh g−1 (82 % retention) and 116 mAh g−1 (68 % retention) after 50 and 100 cycles, respectively, at low current (40 mA g−1). A higher Mg dopant quantity led to improvements in cyclability and rate performance albeit with lower initial discharge capacity. Electrochemical and physical (ex situ XRD) characterizations were used to delineate the role of high‐voltage phase transitions, SEI layer formation, electrolyte solvent insertion into sodium slabs, and active material degradation/dissolution toward capacity loss.

Reusable CuFe2O4–Fe2O3 catalyst synthesis and application for the heterogeneous photo-Fenton degradation of methylene blue in visible light

Abstract Mixed iron and copper oxides were synthesized by the modified Pechini method. Calcined (at different temperatures), characterized and used for the removal of methylene blue dye (MB) by solar photocatalysis. The materials exhibited magnetic behavior and low values of surface area (0.1 to 42.2 m2. g−1). According to the diffuse reflectance spectra, the prohibited band intervals of the samples ranged from 1.92 to 2.4 eV. The results of the X-ray diffraction analysis showed that the hematite and copper ferrite phases were the main responsible for the high efficiency of the photochemical reaction, with apparent kinetic constant equal to k =0.016 min−1 and 100% removal of the dye in 180 min of reaction (starting from an initial solution with 50 mg.L−1 of the dye). MB removal from the aqueous solution occurred in the presence of H2O2 (with 300 mg.L−1), with 1.0 g.L−1 of catalyst, at neutral pH and under solar radiation. The stability of the catalyst was confirmed by its reuse in four consecutive cycles. A kinetic mechanism for photochemical reaction has been proposed, which explains the experimental results obtained.

Nd3+ concentration effect on luminescent properties of MgAl2O4 nanopowders synthesized by modified Pechini method

In this paper, the concentration series of MgAl2O4:Nd3+ nanocrystalline powders have been synthesized by modified Pechini method. Neodymium doping concentration was varied within range of 0.05–5 ​at.%. The obtained samples have been analyzed using the various experimental methods: X-Ray diffraction, scanning electron microscopy, energy dispersive X-Ray spectroscopy, as well as steady-state and kinetics photoluminescence spectroscopy. According to XRD, all synthesized samples are monophasic without any structural impurities. The doping concentration effect on the luminescent characteristics of MgAl2O4:Nd3+ nanocrystalline particles has been studied in terms of emission intensity and lifetime. The optimal doping Nd3+ concentration was determined to be 0.1 ​at.%. Concentration quenching in MgAl2O4:Nd3+ powders occurred via energy transfer among the nearest neighbor ions. Performed studies shed the light on behavior of Nd3+ ions in nanoscale magnesium aluminum spinel.

Thickness-dependent and tunable mechanical properties of CaTiO3 dielectric thin films determined by nanoindentation technique

Microwave dielectric CaTiO3 thin films were deposited on Pt/Ti/SiO2 coated Si substrates by a Pechini method. Crystal structures and morphologies of the CaTiO3 films were characterized by XRD and SEM, which confirms the pure perovskite phase, uniform thickness and smooth surface of the as-obtained thin films. Intrinsic mechanical characteristics of the CaTiO3 films were tested by nanoindentation method and were found to be strongly thickness dependent. The film modulus was found to decrease from 200 GPa (65 nm) to 189 GPa (250 nm) and then increase to 228 GPa (340 nm). The hardness improved monotonically from 15.6 (65 nm) to 21.7 GPa (340 nm). Our study suggests that the mechanical properties can be effectively tuned by film thickness and hence grain size control and may promote the design of high performance microwave dielectric devices for future applications.

Spectroscopic and kinetic insights into the methane reforming over Ce-pyrochlores

High thermal stability and oxygen conductivity of pyrochlores makes them a potential catalyst for the dry reforming of methane (DRM). In this study, noble metal (Pt, Ru) substituted Ce2Zr2O7 and Ce2Ti2O7 pyrochlores have been synthesized by modified Pechini method. The effect of variation of dopant concentration and position was examined to achieve strong metal-support interaction. Ce2Zr1.96Pt0.04O7-δ exhibited the best catalytic activity towards DRM and hence, been studied for partial oxidation (POM) and autothermal reforming of methane (ATR). Syngas ratio (H2/CO) was tuned by varying the O2 concentration in the feed. Insights obtained from both ex-situ and in situ characterization were exploited to discern the reaction mechanism. The surface intermediates were examined by DRIFTS on Ce2Zr1.96Pt0.04O7-δ for DRM, POM and ATR. Besides adsorbed CH4 and CO on Pt, the presence of carbonate and formate species were also identified. Thus, a dual-site mechanism via carbonate and formate formation was proposed for DRM over Ce2Zr1.96Pt0.04O7-δ.

Synthesis and luminescence properties of YVO4: Nd3+, Er3+ and Tm3+ nanoparticles

In this work we report on YVO4 nanocrystalline powders doped with individual ions Nd3+, Er3+ and Tm3+, and their combination. Modified Pechini method allowed obtaining weakly agglomerated single phase nanoparticles with average size of 50 nm. Luminescence properties of single and triply doped YVO4 nanoparticles were studied under selective excitation via individual ions and combined excitation via host material. The obtained results demonstrated intra-centers energy transfer processes for the selective excitation, and set of luminescence bands corresponding to all lanthanides under host excitation in the triply doped system.

Synthesis of silver manganese tri-vanadate AgMn2V3O10 and its catalytic activity on the conversion of para-nitrophenol to para-aminophenol

In this work, we deal with the catalytic activity on the conversion of para-nitrophenol (PNP) to para-aminophenol (PAP) using the synthesis silver, manganese-based tri-vanadate namely AgMn2V3O10 in the presence of sodium borohydride NaBH4. The catalyst was synthesis through the Pechini method; the obtained powder was characterized by X-ray powder diffraction, infrared spectroscopy, scanning electron microscopy. Rietveld refinement was accomplished into XRD data using Jana2006 software, the IR depict V3O10 groups and confirm the catalyst constitution. The morphology was investigated via scanning electron microscopy and shows a homogenous with micrometric particles sizes. Visible UV spectroscopy was used to follow the conversion of para-nitrophenol to para-aminophenol.

Effect of heat treatment on the structure and photocatalytic properties of BiYO3 and BiY0.995Ni0.005O3 ceramic powders

BiYO3 powders were synthesized by the Pechini method under low-temperature conditions. When the heat treatment was performed at T < 600 °C, a mixture of tetragonal and cubic phases was obtained, while for T ≥ 600 °C, only the fluorite-like cubic phase was observed. Based on the Rietveld refinement, approximately 2% and 1% of the tetragonal phase remained in samples calcined at 400 °C and 500 °C for 1 h, respectively. The crystal size calculated for these samples was 4.4–48.1 nm, depending on the calcination temperature. The specific surface area of the samples diminished with heat treatment and reached a minimum at 800 °C. The band gap of samples with mixed phases was close to 2.16 eV and was ~2 eV for samples with a cubic phase. Photocatalytic tests demonstrate that BiY0.995Ni0.005O3 calcined at 800 °C had the best performance: it degraded more than 80% of the antibiotic oxytetracycline when irradiated with visible light. The Ni-doped BiYO3 material could degrade the antibiotic in tap water at an environmentally relevant concentration (μg L−1 levels) and showed steady activity throughout four reaction cycles.

Cathode Performance Study of La0.6Sr0.4Co0.8Fe0.2O3-δ with Various Electrolyte-Doped Ceria Ce0.8Sm0.17Ln0.03O1.9 for IT-Solid Oxide Fuel Cell

La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) cathode perovskite prepared by a Pechini method deposited on ceria co-doping Ce0.8Sm0.17Ln0.03O1.9 (LnSDC), with (Ln = La, Y, and Nd) electrolytes was successfully prepared by the solid-state reaction method. In this preparation process, thick and thin films of LSCF were deposited upon dense Ln-doped ceria LnSDC electrolytes after 5 and 3 spin-coating and dip-coating cycles, respectively. Two layers of LSCF were deposited by screen-printing in order to obtain thick cathode films. After deposition, some structural and morphologic characterizations, such as X-ray diffraction analysis and scanning electron microscopy, have been conducted to understand the properties of the elaborated samples and to study the impact of doping on these properties. Electrochemical impedance spectroscopy measurements on symmetric cells were also performed to investigate the employability of L0.6Sr0.4Co0.8Fe0.2O3-δ as a cathode material deposited upon LnSDC electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFC). According to what was available and inferred after studying the images from a scanning electron microscope, no cracks or significant segregation were detected in the LSCF/LnSDC interface. This behavior is consistent with the good thermal expansion compatibility between the two materials. Electrochemical impedance spectroscopy investigations at 700°C, indicate relatively low area-specific resistance between 0.048 and 0.1 Ω cm2 for all symmetrical cell LSCF/doped electrolyte/LSCF. All the cells were previously sintered above 1400°C, in air. All these results showed that L0.6Sr0.4Co0.8Fe0.2O3- δ can stand as a potential candidate for new cathode material in IT-SOFCs.

Lithium ionic conductivity of Li7-3xFexLa3Zr2O12 ceramics by the Pechini method

Li7La3Zr2O12 (LLZO) with garnet structure has been acknowledged as a promising solid electrolyte for the next generation Li-ion batteries owing to its high chemical stability against Li metal and relatively high Li-ion conductivity. In this work, Li7-3xFexLa3Zr2O12 ceramics were prepared by the Pechini method. The influence of Fe substitution on the structure and microstructure of LLZO powder and ceramic were investigated by X-ray diffraction (XRD), TG (DSC)-MS, Raman spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy. TG-MS and XRD results indicated that LLZO powder could be formed around 750 °C. SEM results showed that the introduction of Fe accelerated densification of LLZO ceramic. The relative density of the composition with x = 0.2 was approximately 95.6%. Its ionic conductivity and activation energy were 4.28 × 10−4 S/cm and 0.27 eV at 30 °C, respectively.